@mom2collegekids USMLE step 1 was the hardest test I have taken in my whole life just because of the sheer breadth of material covered. Hard to believe that was 20 years ago!
Fortunately, I took a 2 week prep class before the test called Arcventures that distilled the content to a manageable amount and for that reason I pulled off the second highest USMLE step 1 score in my class. The guy who beat me did Arcventures too!
If Arcventures still exists, I highly recommend it.
And yes - it is normal to want to puke before, during and after the exam!
PS - I bet your son did better than he thinks!